Study on Tribological Characteristics of Ultra-High Molecular Weight Polyethylene under Unsaturated Lubrication of Water and Brine

Abstract

The tribological characteristics of ultra-high molecular weight polyethylene (UHMWPE) under unsaturated lubrication of water and brine were studied. The friction coefficients and wear rates of UHMWPE at different applied loads and sliding speeds were recorded by field tests, and the effects of load and speed on the friction properties of UHMWPE were analyzed. The results showed that under certain liquid drop (about 150–170 mL/h) lubrication, the tribological behaviors of UHMWPE were better than those of dry sliding, and the friction coefficient and wear rate of UHMWPE were reduced by more than 39% and 10% respectively. The lubrication form of UHMWPE gradually transited from saturated lubrication to unsaturated lubrication with the increase in applied load or sliding speed. The evaporation of water caused by frictional heat affected the water content between the surface of UHMWPE and the counterface, which was the main reason for the change in the lubrication form. In the current work, the critical values for the change of lubrication mode were 70 N and 700 r/min for load and speed, respectively, beyond which UHMWPE was in unsaturated lubrication. Under brine-unsaturated lubrication, the anti-friction property of UHMWPE was better than that in water-unsaturated lubrication at high speed because the precipitated salt granules played a ball effect, which was opposite to that under saturated lubrication. The study of the wear resistance with surface profiler showed that the wear rate of UHMWPE under water-unsaturated lubrication was 9% lower than that under brine-unsaturated lubrication at 110 N load. While the wear resistance of UHMWPE under brine-unsaturated lubrication was better than that in water-unsaturated lubrication at high speed, the wear rate of UHMWPE under brine-unsaturated lubrication was 10% lower than that under water-unsaturated lubrication at 1100 r/min speed.